Conventionally, data recorders have been proposed for recording data from a computer on a recording medium or for transferring data read from the recording medium to the computer. Specifically, referring to FIG. 1, a data recorder 3 temporarily stores digital data transferred thereto from a host computer 1 through a transfer line 2 into a buffer memory unit 4 provided therein, and then records the digital data temporarily stored in the buffer memory unit 4 on a tape by a recording means provided in a data recording unit 5, for example, a digital tape recorder.
Data read from the recording means provided in the data recording unit 5 is temporarily stored into the buffer memory unit 4 and then transferred to the computer 1 through the transfer line 2.
In the configuration shown in FIG. 1, generally, since a data processing speed of the computer 1 does not necessarily match with a recording or reproducing speed of the data recording unit 5, a remaining capacity of the buffer memory unit 4 (an amount of free region in which data can be recorded) is detected upon recording or reading data in the data recording unit 5, such that the recording or reproducing operation of the recording means in the data recording unit 5 is controlled based on the remaining capacity to carry out the data transfer between the computer 1 and the data recording unit 5 without dropping any data.
In practice, an interface in conformity to the SCSI (Small Computer System Interface, ANSI X3.131-1986) standard, for example is used as an interface between the data recorder 3 and the computer 1. Also, employed as the data recording unit 5 is an apparatus for recording digital data on recording tracks helically formed on a tape for digital VTR (Video Tape Recorder) use.
The conventional data recorder 3 of the above-mentioned type has a problem in that since the driving mechanism of the data recording unit 5 is controlled only in accordance with a remaining capacity in the buffer memory unit 4, data cannot be transferred in an optimal condition in terms of average data transfer speed.
Giving supplementary explanation for better understanding, an amount of data transferred from the computer 1 to the data recorder 3 or a data transfer speed at which data is transferred from the computer 1 to the data recorder 3 is not constant depending on a data processing state in the computer 1. Thus, it is difficult to practically predict the timing and speed at which data is transferred from the computer 1.
On the other hand, when a tape is used as a recording medium for the data recording unit 5, data supply to the data recording unit 5 must be started at a timing at which the tape run is started (at the timing at which the head of a track to be recorded-reaches), and the data recording unit 5 must be continuously supplied with data at a fixed speed (for example 10M [bytes/sec]). As a result, if data to be supplied is exhausted in the buffer memory unit 4, the recording in the recording unit 5 must be once stopped. Then, the tape is rewound for a head point search and is run from the head point at a timing at which data supply is started again such that the data recording is resumed in synchronism with the tape running.
Thus, the buffer memory unit 4 provides a function of matching the processing operation of the computer 1 with the processing operation of the data recording unit 5. However, if the driving mechanism of the data recording unit 5 is controlled only in accordance with a remaining capacity of the buffer memory unit 4 as before, the data transfer speed cannot be effectively controlled.
Also, when a tape is used as a recording medium for the data recording unit 5, the tape must be released from tension applied thereto, a rotary drum be stopped, and so on when data cannot be supplied from the buffer memory unit 4 to the data recording unit 5.
It should be understood that if a tape is stopped for a long time in a tension applied state with a rotary drum being rotated, the tape is very likely to be damaged. For this reason, when the supply of data from the buffer memory unit 4 to the data recording unit 5 is interrupted, the data recording unit 5 must be properly controlled to release the tape from the tension and simultaneously stop the rotary drum (this controlled is called the "standby-off"). Then, at the time the data supply is resumed, the data recording unit 5 must be properly controlled to apply the tape with the tension and simultaneously rotate the rotary drum (this control is called the "standby-on").